The Mafia plotted to blow up the Leaning Tower of Pisa, getting as far as preparing the explosives for the strike more than 20 years ago, a court in Palermo has heard.

The plot was hatched in 1992, when the Mafia had declared war on the state, embarking on a series of attacks on police and judges, as well as civilian targets such as museums and trains.

Supergrass Gioacchino La Barbera told the court on Wednesday how convicted terrorist Paolo Bellini suggested the target to his mafia associates, during the years of terror.

Bellini, nicknamed The Black Primrose, said that they should stop bombing civilian targets and hit Italy’s artistic treasures instead.

The court heard how he persuaded boss Nino Gioe that the impact of such a blast would be more powerful, saying: ‘Just imagine. What if Pisa woke up and the Tower wasn’t there!?’

The explosives that were prepared for the attack were eventually discovered by the police.

But the plot was shelved after sweeping arrests in 1993, including that of Sicilian godfather Toto Riina, the court was told.

The mayor of Pisa said Italy must ‘remain vigilant’ in the security of its national monuments.

‘These are chilling revelations,' he said. 'That the blind criminal brutality of the Mafia had put in place plans for a strike on the Leaning Tower, the bell tower of our Cathedral, the symbol of Italy in the world and a world heritage site is the clearest sign of their character.

'This is the same hatred with which they have scarred other monuments and carried out massacres.’ The Leaning Tower will now become a symbol of the fight against criminality, he said.

Tourists visit the Leaning Tower of pisa in April 2011, after it became free of scaffoldings for the first time after 20 years of stabilization and restoration works

The Black Primrose: Paolo Bellini, (pictured left and right) suggested the targets, convincing the boss by saying: 'Just Imagine. What if Pisa woke up and the Tower wasn't there!?'

The boss of bosses: The plot to blow up the Leaning Tower of Pisa was shelved when multiple members of the Mafia were arrested, including Salvatore 'Toto' Riina (pictured during a trial in Rome in 1993)

The supergrass was speaking at a trial in which representatives of the Italian state are accused of signing a peace treaty with the mafia in the 1990s.

Bellini was the go-between, working on a deal between representatives of the state and Cosa Nostra, giving some mafia bosses home or hospital arrest instead of prison, in exchange for revealing the whereabouts of stolen artworks of value, the court heard.

The 170 ft bell tower was begun in the 12th century but immediately began to lean because of soft ground on one side. Following corrective work to stabilise it, the eight storey tower is now leaning slightly less. It brings in six million visitors to Pisa every year.

Not so leaning tower: These side by side pictures show the tower before the stabilization works in 1992 (left) and at the end of the works in 2010 (right), showing a slightly different level of tilt